Various devices are known for dispensing a volatile liquid. For example, an air freshening dispenser device is known from the document U.S. Pat. No. 5,749,519. This device relates to an air freshener that has a reservoir for containing an air freshener liquid. The reservoir is connected to a vapour-emanating surface of a liquid dispensing device by way of a wick. The vapour emanating surface is initially covered with a peal-off seal means. Once the seal means pealed off, the liquid is transmitted from the reservoir via the wick through capillary action directly to the vapour-emanating surface so as to dispense the air freshener.
Due to its design, and in particular due to the use of capillary action and wicking pressure, the liquid dispensing device always transmits the liquid to the vapour-emanating surface means. Thus, to avoid the ensuing waste and spill, the device is provided in a housing having a cover for sealing the vapour-emanating surface means. Once the cover is removed, the vapour is continuously dispensed into the surrounding air. Hence controlled release of the evaporation is not possible.
This leads to excessive dispensing of liquid if one does not want to fragrance a room for example, but forgets to put the cover back on, and it becomes impossible to allow for a controlled dispersion of the vapour amount. It further leads to the phenomenon of olfactory fatigue, a condition where one does not perceive the refreshing odour any longer because of habituation.
Another device is known from the document U.S. Pat. No. 5,662,835 in which a liquid chemical agent is transported from a supply to an emanating surface from which an airflow provided by a ventilator facilitates the diffusion of the liquid chemical agent into the air. The document discloses means for interrupting the transportation of the chemical agent from the supply to the emanating surface. The means for interrupting the transport of the chemical agent are described as being provided initially and then being broken as soon as the device is put into service, much like disclosed by the previous document. From then on the device always emits the chemical agent at some significant level, unless an additional closure is provided. The level can be further modulated by the use of a fan, but can in principle only be increased above a base level.
Another device is known from the document U.S. Pat. No. 6,341,732 in which the liquid to be expelled is supplied from a wick straight up to the underside of a superposed vibrating dome-shaped orifice plate where the liquid flows through capillary action through orifices in the plate and is then ejected in a timed fashion from its upper side through the action of the vibrating orifice plate. Liquid which passes through the orifices in the dome region of the plate, but which has not been ejected, is directed back down through larger openings in a lower region of the plate. The liquid also flows back onto the wick, which places it in continuous capillary communication along the underside of the plate with the atomizing orifices. In this context, corresponding document WO01/97982 relating to the same device is more explicit regarding that sort of functionality.
Thus this device actually has a 2-phase mode of continuous function:                a) continuous evaporation as described above, and        b) additional timed ejection via the vibrating orifice plate        
The continuous evaporation alone can be found to be in the range of 100 mg/day without any piezo actuated time emission. Consequently the device has the problem of in fact never being off, but diffusing at a continuous rate and dispensing in a timed fashion at a higher rate. This, as with the previously cited device, leads to the phenomenon of olfactory fatigue, where the user doesn't notice the odour anymore over time and where the fragrance including the solvents are actually continuously and uselessly dispensed in the air. Also, this device requires a complicated construction to hold the plate vibration actuation means at a particular distance from the wick. The device has a further problem in that because of the continuously wet outside surface of the orifice plate, some larger droplets might be expelled, which can cause the liquid to fall-out, meaning not being ejected in the air to evaporate but falling back on the surface where the device is placed. Additional problems result from the fact that the outside surface of the orifice plate actually accommodates the piezoelectric vibrating element and the connectors and that the continued liquid and solvent supply over these surfaces requires particular attention in order to provide long-term reliability. Avoiding this problem leads to complicated surface treatment and electronics and to a certain limitation of liquids that can be expelled without this phenomenon of fall-out and other functional decay. This device further has a problem of causing a wetting of fingers or hands of a user when changing the disposable reservoir. Further, it is very difficult to control the amount of liquid ejected, which is why peripheral orifices are provided to recuperate liquid that has not been ejected.
Additional features of the same known device are disclosed in document U.S. Pat. No. 6,439,474, introducing a battery driven piezoelectric atomizer that is controlled by decreasing vibration amplitude and by executing a frequency sweep during the decreasing amplitude.
In this device the liquid is supplied by a wick from a reservoir directly to the domed region in the underside of a circular membrane that is vibrated by an annular piezoelectric actuator in known fashion. The vibration is controlled by a driving sequence, where driving and sleeping periods of differing lengths alternate. The battery supply voltage of 1.5 Volt is first increased via a charge pump to 3.3 Volt, related to the highest vibration amplitude. The drive period starts initially at the highest voltage supplied by the charge pump, which then decreases as determined by an RC timing circuit. Hence the voltage decrease happens exponentially as given by that sort of circuit and determines the duration of the fixed drive period. Its lowest level is chosen to still ensure proper functioning of the device. During part of the sleep period, the battery is recharged to allow for a further drive period. Different intensities are programmable by varying the duration of the sleep period. As said before, during the sleep period the device continues to evaporate the liquid passively in the particular passive evaporation mode of the 2-phase mode of continuous device function. The device further uses a frequency sweep mode to accommodate for inter-device device variations.
Another droplet spray device is known from the document U.S. Pat. No. 6,062,212 which describes a liquid dispenser having vibration means which are activated to expel a metered dose of liquid deposited on a mesh from that mesh in the usual manner. The vibration means remain activated longer than necessary to expel the metered dose of liquid to ensure a complete emptying of the liquid from the dispenser. The disadvantage is that this additional atomising duration will sometimes be either too long or too short and that a fixed time will not work with liquids of varying viscosities, surface tensions and ambient conditions, as is the case with liquids containing volatile solvents.
Another atomising device is known from the document WO 03/082477 A1, disclosing the surface treatment of the outer side of a vibrating orifice atomizer in such a manner as to resist wetting and liquid build-up.
Another device is known from the document U.S. Pat. No. 4,702,418 which describes a piezoelectric aerosol dispenser that has eccentric liquid inlet/outlet means, and a nozzle chamber having a nozzle region proximate a single nozzle and a larger reservoir interconnected to the nozzle region. The nozzle region is gravity fed through a restrictive channel. Further, a piezoelectric bender is used to drive fluid from the reservoir region to the nozzle region and from the nozzle region through the single nozzle to create an aerosol spray. Such an arrangement with a piezoelectric bender does not allow for a controlled release of fluid, as the fluid must first be pumped from the reservoir region and then expelled from the nozzles without interference of one flow with the other. Further, precise control while using a piezoelectric bender is virtually impossible.
Another device is known from the document EP 1 150 779 which describes a piezoelectric spraying system for dispensing volatiles. The atomisation method relates to a device that uses a wick to transfer a liquid to a vibrating orifice plate, the liquid having certain characteristics known from fragrance formulations.
Yet another device is known from EP 1 430 958 which discloses a liquid supply package comprising a liquid container with a wick extending just above the top of the container and supplying liquid having basically the same characteristics as noted in the previous document.
It should be noted that in both these cases as well as other prior art wick-fed atomizers using a vibrating orifice plate as outlet means with generally tapered shaped orifices, the vertical and centric liquid feeding arrangement always needs to put the liquid feeding point underneath the outlet means. This has two drawbacks. The shape of the orifices facilitates oozing, increased passive evaporation and the position of the wick with regards to the outlet means limits the height and volume of the container via a particular wick length at which reliable continuous feed can still be achieved, specially over a certain range of viscosity and density. In fact applicant has observed that as of a particular height of reservoir or length of wick, the liquid does no longer get to a feeding point underneath the outlet means, but flows back into the reservoir and hence “starves” the atomizer. Consequently, the resulting devices are known to have very small and low profile liquid containers, limiting the useful life of a refill and also need particularly volatile ingredients with potentially ensuing VOC problems.
Document WO 2005/097349 discloses a very similar device using a compressible wick with a compliant upper wick section in direct contact with the vibrating orifice plate.
Other devices are disclosed which deliver several volatile liquids and coordinate delivery with light, sound, motion, temperature and the like such as WO 03/09871 and WO 04043502, where however the continuous evaporation persists and hence also the problems of olfactory fatigue and unsatisfactory delivery control. These devices therefore appear at odds with the objective of creating a precise ambiance at a particular time depending on and in coordination with sound, light and the like. Indeed the efficiency of olfactory sensorial performance hinges on the effect that “now the scent is not present”; and “suddenly, i.e. shortly after a particular musical theme or shortly after turning on the lights” and the like, it is present.
It is, therefore, an object of the present invention to provide a volatile liquid dispenser device that overcomes the abovementioned inconveniences of olfactory fatigue, of continuous evaporation of fragrances and solvents, of insufficient delivery control, of reservoir limitations and of fall-out.
It is a further objective of the present invention to provide controlled release of liquid substances such as fragrances, aromas, hydrolates, essential oil formulations, non-aqueous solvent based liquids and certain aqueous liquids including those containing surfactants, medication agents and the like, dispensed in very small droplets by such a device.
It is another object of the present invention to provide such a device that is simple in construction, reliable and inexpensive to manufacture, small in size, flexible with regards to liquid properties and reservoir volume as well as low in energy consumption and cost.